[0001] The present invention is directed to a new silicon oxycarbide (SiOC) composite material
in microparticulate form useful as electrode active material, in particular for a
lithium-ion battery anode, and method for producing such a SiOC particulate material.
These electrodes can be used to form batteries with high capacities and long-time
stability upon cycling.
[0002] Lithium-ion batteries are widely used as electric sources for example for lap top
computers, cellular phones and camcorders. Rechargeable lithium ion batteries have
a simple mechanism. During charge, lithium ions are extracted from the cathode and
inserted as lithium into the anode. On discharge, the reverse process occurs. The
electrodes used in these batteries are very important and can have dramatic effects
on the batteries performance.
[0003] The most common anode materials to date have been carbonaceous compounds such as
graphite. Unfortunately, conventional graphite anode material faces limitation due
to low theoretical specific capacity of 372 mAh.g
-1.
[0004] Yet, cells with larger capacities are often required for high energy applications
of Li-ion batteries.
[0005] In order to improve the capacity of the batteries, studies have been conducted to
replace graphite anode material in Li-ion batteries. In this respect, silicon has
shown promising results thanks to its very high theoretical capacity (3600 mAh.g
-1). However, lithium insertion into bulk silicon material causes large volume expansion
leading to fast loss of performance upon charge/discharge cycling.
[0006] Among several alternatives, silicon oxycarbide (SiOC) materials can be of great interest
and various works about synthesis of such materials have been reported in the literature.
[0007] For example, Fukui
et al. [1] proposed to prepare SiOC material for anode application from the pyrolysis of
polysilane material (Ph
2Si)
0.85(PhSi)
0.15. They also studied the result of pyrolysing a mixture of polysilane starting material
with polystyrene, and showed that it leads to the formation of a SiOC composite containing
electrochemically active free carbon and having microporosity that enables better
electrochemical performance than the one obtained from pure polysilane. This material
thus offers a first lithiation capacity of about 850 mAh.g
-1 and a first coulombic efficiency of 70%. The influence of phenyl substituents in
polysilane precursors on SiOC microstructure [2], or of pyrolysis temperature on lithium
storage performance of SiOC material ([3], [4]) has also been investigated. It has
been shown that a material prepared by pyrolysing at 700°C displays improved performance
with an average capacity of around 450 mAh.g
-1, whereas high pyrolysis temperatures lead to the formation of inactive crystalline
SiC phase and increased carbon organization providing less Li-ion storing sites, thus
to degraded electrochemical performance. Mention may also be made of document
EP 2 104 164 relating to the aforementioned studies that reports the production of a porous silicon
oxycarbide material by carbonizing both a silicon metal or a silicon-containing compound
such as polysilane, and an organic compound containing no silicon atoms and having
a softening point or a melting point, in an inert gas or in a vacuum at a temperature
ranging from 300°C to 1,500°C, for example polystyrene.
[0008] Following a similar approach,
Dahn et al. (EP 0 867 958) propose silicon oxycarbide electrode materials for lithium ion batteries produced
from the pyrolysis of a silicon-containing preceramic polymer. The obtained SiOC material
is thereafter treated with a strong acid or a strong base to reduce the Si and O contents
as well as increase the surface area and open porosity.
[0009] However, the currently proposed silicon oxycarbide materials display insufficient
electrochemical performance in practical use for the desired high energy Li-ion battery.
[0010] Consequently, there remains a need to produce silicon-based materials for electrodes,
in particular for lithium-ion battery anode, capable of insuring high capacity and
long time stability upon cycling.
[0011] The present invention specifically aims to provide a new silicon oxycarbide composite
material as electrode active material that satisfies the aforementioned requirements.
[0012] In particular, the present invention relates, according to a first one of its aspects,
to a SiOC composite material in microparticulate form, characterized in that the microparticles
are formed, in whole or in part, of an amorphous SiOC matrix with Si ranging from
20 wt% to 60 wt%, O from 20 wt% to 40 wt% and C from 10 wt% to 50 wt%, in which amorphous
or crystallized silicon particles are embedded.
[0013] According to a particular embodiment, the microparticles are of core/coating type
with a core formed of said amorphous SiOC matrix and coated with at least one amorphous
carbon layer.
[0014] Against all expectations, the inventors have discovered that such a particulate SiOC
composite material can provide the batteries with highly desirable properties in terms
of high capacity and cycle durability.
[0015] Thus, according to another of its aspects, the invention relates to the use of a
SiOC composite material as defined above as an electrode active material. Another
subject of the present invention is also an electrode active material comprising at
least the aforementioned SiOC composite material.
[0016] The invention also relates to an electrode comprising such an electrode active material.
[0017] An electrode active material in accordance with the invention is particularly suitable
for an anode electrode, in particular for a lithium-ion battery, and especially for
a lithium-ion secondary battery.
[0018] Thus, according to still another of its aspects, an object of the present invention
is a battery, in particular a lithium-ion secondary battery, comprising an electrode,
preferably a negative electrode, using the aforementioned SiOC composite material.
[0019] Advantageously, the electrode active material according to the invention makes it
possible to attain improved electrochemical performances both in terms of superior
reversible capacity and cycle durability, as demonstrated in the examples that follow.
More particularly, the electrodes formed from said SiOC composite material have the
ability to store large quantities of lithium. Further, the initial capacity of the
battery can be maintained through several charge/discharge cycles of the battery.
In particular, a lithium-ion battery using a SiOC composite material according to
the invention displays an average capacity higher than 700 mAh/g on a large number
of charge/discharge cycles.
[0020] Moreover, as detailed below, the electrode material according to the invention can
be prepared by a simple preparation method from an industrial point of view. Thus,
it is further an object of the instant invention to provide a method for producing
a SiOC composite material according to the invention.
[0021] Other features, advantages and modes of application of the SiOC composite material,
process for its preparation and their implementation according to the invention will
emerge more clearly on reading the following description and examples.
[0022] In the remainder of the text, the expressions "between ... and ...", "ranging from
... to ..." and "varying from ... to ..." are equivalent and are understood to mean
that the limits are included, unless otherwise mentioned.
SiOC COMPOSITE MATERIAL
[0023] As emerges from the foregoing, the SiOC composite material according to the invention
is made of microparticles formed, in whole or in part, of an amorphous silicon oxycarbide
network of formula SiOC, also referred to as "SiOC matrix", where Si ranges from 20
wt% to 60 wt%, O ranges from 20 wt% to 40 wt% and C ranges from 10 wt% to 50 wt% based
on the total weight of the SiOC matrix.
[0024] Although unaccounted for in the formula "SiOC matrix", hydrogen may also be present
in trace amounts, in particular less than 2 wt% based on the total weight of the SiOC
matrix.
[0025] Amorphous or crystallized silicon particles are trapped in said SiOC matrix. Preferably,
said silicon particles are uniformly distributed in the SiOC matrix.
[0026] Said amorphous or crystallized silicon particles may have an average size ranging
from 2 nm to 2 µm, in particular from 50 nm to 800 nm. Said particle size can be determined
by known methods, for example by the laser diffraction technic or SEM observation.
[0027] More particularly, said silicon particles may be present in the SiOC matrix in a
weight ratio SiOC matrix/Si particles ranging from 2 to 20, in particular from 5 to
15.
[0028] In a particularly preferred embodiment variant, the silicon particles embedded in
the SiOC matrix are in crystallized form. Within the context of this variant, the
crystallized silicon has more particularly a cubic crystalline structure. This may
be evaluated by X-ray diffraction analysis.
[0029] According to an embodiment variant, the microparticles are formed of the amorphous
SiOC matrix in which amorphous or crystallized silicon particles are embedded.
[0030] According to another embodiment variant, the microparticles are of core/coating structure.
More particularly, they may have a core formed of said amorphous SiOC matrix and coated
with at least one amorphous carbon layer.
[0031] The core of microparticles according to this particular variant formed by the silicon-enriched
SiOC matrix may have an average particle size, for example obtained by laser diffraction
analysis, ranging from 1 µm to 100 µm, in particular from 5 µm to 50 µm.
[0032] The silicon-enriched SiOC core may be coated by an amorphous carbon layer.
[0033] In particular, the coating rate may be less than or equal to 50 wt%, more particularly
comprised between 10 wt% and 30 wt%.
[0034] The carbon layer formed at the surface of the silicon oxycarbide cores may have a
thickness ranging from 1 nm to 200 nm, and especially from 5 nm to 50 nm.
[0035] Without wishing to be bound by the theory, it can be assumed that the carbon coating
acts as relaxing agent for volume change during the cation insertion/extraction (for
example lithium insertion/extraction in the case of a lithium-ion battery), thus enabling
improved cycle durability.
[0036] The particulate SiOC composite material of the invention may have an average particle
size ranging from 1 µm to 100 µm, in particular from 5 µm to 50 µm.
[0037] The average particle size may be obtained by laser diffraction analysis according
to a technique known to a person skilled in the art.
[0038] According to a particular embodiment, the aforementioned composite material presents
a specific surface area measured by the Brunauer Emmett Teller (BET) method ranging
from 1 m
2/g to 100 m
2/g, preferably from 1 m
2/g to 55 m
2/g.
[0039] Further, advantageously, the microparticles of the material of the invention have
a globally spherical shape (without considering the irregularities of the surface).
Preferably, the SiOC composite material of the invention is a material in which the
adsorption isotherm of nitrogen is classified into TYPE III defined in IUPAC. This
also means that the microparticles forming the composite material of the invention
are nonporous.
METHOD FOR PRODUCING THE SiOC COMPOSITE MATERIAL
[0040] According to another of its aspects, the invention relates to a method for producing
a particulate SiOC composite material, in particular as described above, comprising
at least the steps, in that order, of:
- (i) providing a product consisting of at least one silicon-containing polymer enriched
in amorphous or crystallized silicon particles;
- (ii) pyrolysing the product of step (i) to yield an amorphous SiOC matrix with Si
ranging from 20 wt% to 60 wt%, O from 20 wt% to 40 wt% and C from 10 wt% to 50 wt%,
in which amorphous or crystallized silicon particles are embedded;
- (iii) processing the pyrolysis product obtained in step (ii) into a powder form with
an average particle size ranging from 1 µm to 100 µm;
- (iv) and possibly, forming a carbon coating on the surface of the particles of the
powder obtained in step (iii),
to obtain the desired SiOC composite material.
Step (i): Silicon-loaded polymer material
[0041] As specified previously, step (i) of the process of the invention consists in providing
a silicon-containing polymer material enriched in amorphous or crystallized silicon
particles, referred below as "Si-loaded polymer".
[0042] The silicon-containing polymer used in step (i) of the process of the invention may
be of various natures. In particular, it may be chosen from polycarbosilanes, polysilanes,
polysiloxanes and polysilsesquioxanes.
[0043] Generally, polycarbosilanes contain units of the type (R
1R
2SiCH
2), (R
1Si(CH
2)
1.5) and/or (R
1R
2R
3Si(CH
2)
0.5) where each R
1, R
2 and R
3 is independently selected from hydrogen and hydrocarbons having 1-20 carbon atoms.
The hydrocarbons can include alkyls such as methyl, ethyl, propyl and butyl; alkenyls
such as vinyl and allyl; and aryls such as phenyl. In addition, the hydrocarbon groups
can contain hetero atoms such as silicon, nitrogen or boron. The polycarbosilanes
may also be substituted with various metal groups such as aluminum, chromium and titanium.
The substituted polycarbosilanes are also known in the art and can be manufactured
by known methods.
[0044] The polysilanes useful herein are known in the art and generally contain units of
the formula (R
1R
2R
3Si), (R
1R
2Si) and (R
3Si) wherein R
1, R
2 and R
3 are as described above. Examples of specific polysilane units are (Me
2Si), (PhMeSi), (MeSi), (PhSi), (ViSi), (PhHSi), (MeHSi), (MeViSi), (Ph
2Si), (PhViSi), (Me
3Si) and others, wherein Me is methyl, Ph is phenyl and Vi is vinyl. The polysilane
may also be substituted with various metal groups (i.e., containing repeating metal-Si
units). Examples of suitable metals include aluminum, chromium and titanium.
[0045] The polysiloxanes useful herein are known in the art and are of the structure:
(R
1R
2R
3SiO
0.5)
w(R
4R
5SiO)
x(R
6SiO
1.5)
y(SiO
4/2)
z
wherein R
1, R
2, R
3, R
4, R
5 and R
6 are as described above and w, x, y and z are mole fractions with w=0 to 0.8, x=0.3
to 1, y=0 to 0.9, z=0 to 0.9 and w+x+y+z=1.
[0046] Examples of specific siloxane units include (MeSiO
1.5), (PhSiO
1.5), (ViSiO
1.5), (HSiO
1.5), (PhMeSiO), (MeHSiO), (PhViSiO), (MeViSiO), (Ph
2SiO), (Me
2SiO), (Me
3SiO
0.5), (Ph
2ViSiO
0.5), (Ph
2HSiO
0.5), (H
2ViSiO
0.5), (Me
2ViSiO
0.5), (SiO
4/2) and other wherein Me is methyl, Ph is phenyl and Vi is vinyl.
[0047] Polysilsesquioxanes useful herein are known in the art. Generally, these polysilsesquioxanes
contain units of the type (RSiO
3/2)
x wherein R is a hydrocarbon group, saturated or unsaturated, linear, branched or cyclic,
for example of the type -C
nH
2n+1, with n being an integer ranging from 1 to 20, especially a methyl, ethyl, propyl,
butyl, pentyl, hexyl, heptyl, octyl, nonyl, decyl, dodecyl, tridecyl, tetradecyl,
hexadecyl, octadecyl and eicosyl; an aryl group, especially phenyl or tolyl group;
a cycloalkyl, particularly cyclobutyl, cyclopentyl or cyclohexyl; alkenyl, especially
vinyl or allyl; or aralkyl including 2-phenylethyl or benzyl, R can also contain hetero
atoms, in particular nitrogen or halogen, preferably R is methyl, ethyl, propyl or
phenyl. R may be combination of two or more kinds of different groups. x is the number
of patterns, and can be between 4 and 10,000.
[0048] Within the meaning of the invention, the expression "silicon-containing" polymer
as used herein is intended to include copolymers or blends of the above silicon-containing
polymers and other polymers which are also useful herein. For instance, copolymers
of silicon-containing polymers and silalkylenes (R
2Si(CH
2)
nSiR
2O) such as silethylene, silarylenes such as silphenylene (R
2Si(C
6H
4)
nSiR
2O), silazanes (R
2SiN), silanes (R
2Si-SiR
2), organic polymers and others can be used herein. The silicon-containing polymer,
as described above, may be used alone or in combination with two or more types thereof.
[0049] The silicon-containing polymer is capable to yield under pyrolysis to the aforementioned
amorphous SiOC matrix.
[0050] According to one particularly preferred embodiment, said silicon-containing polymer
is a polysilsesquioxane.
[0051] Preferably, silicon-containing polymers which contain phenyl groups are used.
[0052] By way of example, the silicon-containing polymer used in the process according to
the invention is phenyl-bridged polysilsesquioxane that is (PhSiO
1.5)
n or methyl/phenyl-bridged polysilsesquioxane that is (MeSiO
1.5)
m(PhSiO
1.5)
n.
[0053] The silicon-containing polymer is loaded with amorphous or crystallized silicon particles.
Preferably, silicon particles are in crystallized form.
[0054] Said amorphous or crystallized silicon particles may have an average particle size
ranging from 2 nm to 2 µm, in particular from 50 nm to 800 nm.
[0055] According to a first embodiment variant, the Si-loaded polymer of step (i) may be
prepared by mixing at least one silicon-containing polymer in a solid state, in particular
in an amorphous form, and a crystallized or amorphous silicon powder.
[0056] In particular, said Si-loaded polymer may be produced by mixing both compounds by
mechanical milling, for example using a bowl and balls. Eventually, an organic solvent
(for example, acetone) may be added to facilitate mixing.
[0057] The adjustment of milling conditions falls within the abilities of a person skilled
in the art. More particularly, the mechanical milling may be carried out at a milling
speed ranging from 10 rpm to 1,000 rpm, preferentially from 100 rpm to 400 rpm. The
milling time may be comprised between 1 minute and 100 hours, in particular between
10 minutes and 2 hours.
[0058] Naturally, other blending techniques can be used to get the Si-loaded polymer.
[0059] Thus, according to another embodiment variant, the Si-loaded polymer in step (i)
may be prepared by addition of an amorphous or crystallized silicon powder to silicon-containing
polymer dissolved in a suitable solvent (for example, acetone), followed by spray
drying or evaporation of the solvent.
[0060] According to yet another embodiment variant, the Si-loaded polymer in step (i) may
be prepared by synthetizing the silicon-containing polymer by a sol-gel method in
the presence of a crystallized or amorphous silicon powder, as illustrated in examples
6 and 8 below.
[0061] The sol-gel techniques, in particular the choice of suitable silane precursors to
yield the silicon-containing polymer, clearly fall within the abilities of a person
skilled in the art.
[0062] According to a particular embodiment, the Si-loaded polymer of step (i) may be in
powder form.
[0063] The silicon-containing polymer enriched in silicon particles may be formed into a
powder by means of pulverization treatment or a granulation treatment, if necessary.
The pulverization or granulation methods can be carried out by means of a common pulverizer
such as a ball mill, or a common granulator such as pelletizer.
Step (ii): Pyrolysis
[0064] In a consecutive second essential step of the process of the invention, the product
of step (i), eventually in powder form, is pyrolysed to yield an amorphous SiOC matrix
as specified above in which silicon particles are embedded.
[0065] The pyrolysis may be carried out in an inert or reductive gaseous atmosphere. As
examples of the inert gas, mention may be made of nitrogen, helium and argon. A reducing
gas such as a hydrogen gas may be included in the aforementioned inert gas. For example,
the pyrolysis step may be carried out in argon or argon-H
2. Inert atmospheres are used during pyrolysis to prevent oxygen incorporation into
the silicon oxycarbide matrix or loss of carbon through combustion.
[0066] The adjustment of the temperature and time conditions of the pyrolysis to reach the
desired product falls within the abilities of a person skilled in the art.
[0067] In particular, the product may be pyrolysed by heating to a temperature (finally
reachable temperature) ranging from 600°C to 1,400°C, in particular from 900°C to
1,300°C and more particularly from 1,000°C to 1,200°C.
[0068] The heating rate may range from 1°C/min to 30°C/min, in particular from 2°C/min to
10°C/min to reach the final pyrolysis temperature. The pyrolysis step may be held
to a fixed temperature before reaching the final pyrolysis temperature.
[0069] The heating duration at final temperature may be comprised between 5 minutes and
10 hours, in particular between 30 minutes and 5 hours.
[0070] Pyrolysis of the product may be performed in any conventional high temperature furnace
equipped with a means to control the furnace atmosphere. Such furnaces such as tubular
furnaces are well known in the art and many are commercially available. The product
to be pyrolysed is, for example, fed into a crucible made of quartz or alumina.
[0071] The resultant pyrolysed product, obtainable as a black solid, is formed of an amorphous
SiOC matrix as specified above in which particles of amorphous or crystallized silicon
are trapped.
[0072] The silicon particles may be present in the SiOC matrix in a weight ratio SiOC matrix/Si
particles ranging from 2 to 20, in particular from 5 to 15.
Step (iii): Formation of a powder
[0073] In a third step (iii) of the process of the invention, the pyrolysis product obtained
in step (ii) is ground into a powder having an average particle size in a range of
1 µm to 100 µm.
[0074] A person skilled in the art is able to carry out known techniques to process the
pyrolysis product into the desired powder form, such as by grinding or milling (for
example in ball mill, a jet mill or hammer mill).
[0075] By way of example, the powder may be produced by mechanically milling, for example
by using a bowl and balls.
[0076] The milling speed may range from 10 rpm to 1,000 rpm, in particular from 200 rpm
to 600 rpm. As for the milling time, it may be comprised between 1 minute and 100
hours, in particular between 10 minutes and 2 hours.
[0077] Preferably, the powder of pyrolysis product has an average particle size in a range
of 1 µm to 100 µm, in particular of 5 µm to 50 µm.
Step (iv): Carbon coating
[0078] According to a particular embodiment, the process may finally involve a step (iv)
directed toward coating the powder particles obtained at the end of step (iii) with
an amorphous carbon layer.
[0079] According to one particular embodiment variant, said carbon coating may be formed
by:
- (a) coating the particles with at least one organic carbon precursor containing no
silicon atoms and being able to be transformed into carbon during a pyrolysis process;
and then,
- (b) pyrolysing said coated particles to obtain the carbon coating.
[0080] Organic compounds suitable for forming carbon by pyrolysis are well-known. In particular,
the organic carbon precursor may be chosen from polyvinylidene difluoride (PVdF),
sucrose, chlorinated polyethylene, polyvinyl chloride, polyethylene, phenolic resin,
polyethylene oxide, pitch, polyvinyl alcohol, polystyrene, carboxymethyl cellulose
or a salt thereof, alginic acid, oxalic acid including sodium or potassium salt, polyacrylic
acid or a salt thereof, polyacrylonitrile and polyvinyl fluoride.
[0081] According to one particularly preferred embodiment, said carbon precursor is a polyvinyl
alcohol.
[0082] The coating made of carbon precursor can be formed by conventional methods.
[0083] A person skilled in the art is able to carry out known techniques to form a coating
of carbon precursor on the surface of the particles.
[0084] By way of example, the carbon precursor may be dissolved in a suitable aqueous or
organic solvent. The pyrolysed powder obtained at the end of step (iii) is then added
to the solution of carbon precursor, and the resulting mixture can then be dried,
for example by spray-drying to reach the coated particles.
[0085] The coating of carbon precursor may also be obtained by other standard methods, for
example by chemical vapor deposition technic, mechanical milling or freeze drying.
[0086] The amount of carbon precursor necessary to obtain the carbon coating clearly falls
within the abilities of a person skilled in the art.
[0087] According to a particular embodiment, the carbon precursor is crosslinkable. Within
the context of this variant, the particles coated with said crosslinkable carbon precursor
may be subjected, prior to the pyrolysis step (b), to a pre-treatment, in particular
a heat-treatment, in order to induce the crosslinking of said carbon precursor.
[0088] The heat-treatment may be performed under air at a temperature ranging from 50°C
to 400°C for 1 hour to 30 hours.
[0089] As seen previously for the pyrolysis step (ii), the adjustment of the pyrolysis conditions
in step (b) to yield the desired carbon coating comes within the abilities of a person
skilled in the art.
[0090] In particular, the pyrolysis may be carried out in an inert or reductive gaseous
atmosphere, such as argon or argon-H
2.
[0091] By way of example, the pyrolysis temperature (finally reachable temperature) may
range from 600°C to 1,400°C, in particular from 900°C to 1,100°C.
[0092] The heating rate may range from 1°C/min to 30°C/min, in particular from 2°C/min to
10°C/min to reach the final temperature. The heating duration at final temperature
may be comprised between 5 minutes and 10 hours, in particular between 30 minutes
and 3 hours.
[0093] The final powder has a particle size, obtained for example by laser diffraction analysis,
ranging from 1 µm to 100 µm, in particular from 5 µm to 50 µm.
[0094] As will be seen from the examples below, it is important to follow the steps (i)
to (iii) and optional step (iv) in the order they are presented above to achieve a
final electrode active material that presents improved electrochemical performance.
APPLICATION
[0095] The aforementioned SiOC composite material according to the invention can be used
as an electrode active material for forming an electrode.
[0096] Advantageously, the SiOC composite material is in a powder form, which makes it easier
its use for forming electrodes.
[0097] Preferably, the SiOC composite material of the present invention is suitable as a
material of a negative electrode, in particular for a lithium-ion battery.
[0098] The preparation of an electrode comprising the SiOC composite material of the invention
and its use into the desired battery fall within the abilities of a person skilled
in the art.
[0099] More particularly, the SiOC composite material of the invention may be mixed with
a variety of well-known conductive agents and/or binders to assist in forming the
desired shape electrode.
[0100] In a classic way, an electrode according to the invention can have a collector on
which the active material of the invention is applied. As examples of collector for
a negative electrode, mention may be made of mesh, foil or the like of a metal such
as copper, nickel, or alloys thereof, or the like. The thickness of the electrode
active material on the collector may range from 5 µm to 300 µm, in particular from
10 µm to 100 µm.
[0101] As examples of conductive agents, mention may be made of carbon fibers, carbon black
(such as Ketjen black, acetylene black, or the like), carbon nanotubes, and the like.
[0102] As examples of binders that may be comprised in an electrode according to the invention,
mention may be made of fluorine-based binder, such as polytetrafluoroethylene or polyvinylidene
difluoride binder, polyacrylic acid or a salt thereof, sodium alginate, carboxymethyl
cellulose or a salt thereof, polysaccharides or latex such as styrenebutadiene rubber.
[0103] An electrode according to the invention may comprise any other additives commonly
used in electrodes.
[0104] The electrode according to the present invention can be used in any battery configuration.
According to yet another of its aspects, one subject of the present invention is a
battery comprising an electrode according to the invention.
[0105] As examples of batteries, mention may be made of a lithium ion primary battery, a
lithium ion secondary battery, a capacitor, a hybrid capacitor, an organic radical
battery, or a dual carbon battery.
[0106] As the aforementioned battery, a lithium-ion battery, especially a lithium-ion secondary
battery is particularly preferable.
[0107] The lithium-ion secondary battery can be produced in accordance with conventional
methods. In general, a lithium-ion battery comprises two electrodes, for example a
negative electrode formed from the aforementioned electrode, a positive electrode
capable of charging and discharging lithium and an electrolyte.
[0108] As examples of electrolyte solution, mention may be made of, for examples, lithium
salts such as LiClO
4, LiAsF
6, LiPF
4(C
2O
4), LiPF
6, LiBF
4, LiR
FSO
3, LiCH
3SO
3, LiN(R
FSO
2)
2, LiC(R
FSO
2)
3; R
F being chosen from a fluorine or perfluoroalkyl of 1 to 8 carbon atoms. The salt is
preferably dissolved in a polar aprotic solvent such as ethylene carbonate, propylene
carbonate, ethylmethyl carbonate, dimethyl carbonate, diethyl carbonate, and the like.
It may be supported by a separator sandwiched between the two electrodes. Well-known
separators such as polyolefin-based porous membranes such as porous polypropylene
nonwoven fabric, porous polyethylene nonwoven fabric and the like can be used.
[0109] A person skilled in the art is able to choose the type and amount of the battery
components based on component material properties and the desired performance and
safety requirements of the battery.
[0110] For example, the battery may be in the form of a conventional spiral wound type or
a coin-cell type battery. Other configurations or components are possible.
[0111] The examples and figures which follow are presented by way of illustration and are
non-limitative of the field of the invention.
FIGURES
[0112]
Figure 1: SEM picture of a SiOC composite powder in accordance with the invention synthetized
in example 1;
Figure 2: Particle size distribution diagram obtained by laser diffraction measurement of the
SiOC composite powder synthetized in example 1;
Figure 3: Nitrogen adsorption isotherm of the SiOC composite powder synthetized in example
1;
Figure 4: X-ray diffraction pattern of the SiOC composite powder synthetized in example 1;
Figure 5: Voltage profile obtained with the battery prepared according to example 7 with the
SiOC material synthetized in example 1;
Figure 6: Electrochemical performances (capacity v/s number of cycles) of the batteries prepared
according to example 7 from the materials synthetized in examples 1 to 6;
Figure 7: Electrochemical performances (capacity v/s number of cycles) of the battery prepared
from the SiOC composite material synthetized in example 8.
EXAMPLES
EXAMPLE 1
Reparation of a SiOC composite material in accordance with the invention
[0113] A sample of 28.850 g of amorphous phenyl-bridged polysilsesquioxane compound and
6.053 g of crystallized silicon were put together in a bowl and milled for 1 hour
at a speed of 150 rpm.
[0114] The obtained powder was then pyrolysed under argon atmosphere for 1 hour at 1,000°C.
[0115] After pyrolysis, the sample was recovered and milled at a speed of 400 rpm for 30
minutes.
[0116] The obtained powder was added to an aqueous solution containing PVA (62.5 g/L) dissolved
at 60°C. The obtained mixture was spray-dried at 100°C and a powder was recovered.
[0117] This powder was heat treated at 200°C for 16 hours under air, and then pyrolysed
at 1,000°C for 1 hour under argon atmosphere.
Analysis of the obtained powder
Elemental analysis,
[0118] The silicon content of the obtained powder is measured by inductively coupled plasma
(ICP) emission spectrophotometry. Carbon content is measured by infrared absorption
method after combustion in high frequency induction furnace. Oxygen content is measured
as carbon monoxide and carbon dioxide by a non-dispersive infrared detector.
[0119] The elemental analysis of the obtained powder thus confirms the presence of Si (32.0
wt%), C (36.7 wt%) and O (31 wt%).
SEM analysis
[0120] The observation of the powder by Scanning Electron Microscopy (SEM) (Figure 1) shows
that the particles have a spherical shape.
Laser diffraction analysis
[0121] The particle size distribution obtained by laser diffraction measurement is represented
in Figure 2. The obtained powder has an average particle size of around 10-20 µm.
TEM analysis
[0122] The powder is analyzed by transmission electron microscopy (TEM), and element mapping
obtained from energy dispersive X-ray spectrometry (EDX) measurement in TEM shows
the presence of a carbon coating on the surface of the particles.
Adsorption isotherm of nitrogen
[0123] The nitrogen adsorption isotherm of the obtained powder is shown in Figure 3. This
is classified into TYPE III according to IUPAC.
X-ray diffraction analysis
[0124] The X-ray diffraction pattern of the obtained powder is represented in Figure 4.
It reveals a cubic crystalline silicon phase in the final powder coming from the silicon
particles trapped in the SiOC amorphous matrix.
BET specific surface area
[0125] The BET specific surface area, measured by the nitrogen adsorption technic, of the
obtained powder, is 18 m
2/g.
EXAMPLE 2 (comparative example)
[0126] A sample of 10 g of phenyl-bridged polysilsesquioxane compound was pyrolysed at 1,000°C
for 1 hour under argon atmosphere.
[0127] The recovered sample was then milled at a speed of 400 rpm for 5 min.
[0128] The obtained powder was added to an aqueous solution containing dissolved PVA (62.5
g/L) and dispersed particles of crystallized silicon (27.4 g/L).
[0129] The mixture was spray-dried at 100°C and a powder was recovered.
[0130] This powder was heat treated at 200°C for 16 hours under air and then pyrolysed at
1,000°C for 1 hour under argon atmosphere.
EXAMPLE 3
Preparation ofa SiOC composite material in accordance with the invention
[0131] A sample of 28.850 g of amorphous phenyl-bridged polysilsesquioxane compound and
6.053 g of crystalized silicon were put together in a bowl and milled for 1 hour at
a speed of 150 rpm.
[0132] The obtained powder was then pyrolysed under argon atmosphere for 1 hour at 1,000°C.
[0133] After pyrolysis, the sample was recovered and milled at a speed of 400 rpm for 30
min.
[0134] An amount of 6.25 g of solid PVA was added in the bowl and the mixture was milled
for 1 hour at a speed of 150 rpm. A powder was recovered.
[0135] This powder was heat treated at 200°C for 16 hours under air, and then pyrolysed
at 1,000°C for 1 hour under argon atmosphere.
EXAMPLE 4
Preparation of a SiOC composite material in accordance with the invention
[0136] A sample of 10.070 g of amorphous methyl/phenyl (4/1) bridged polysilsesquioxane
compound, 1.688 g of crystallized silicon and 20 mL of acetone were put together in
a bowl and milled for 1 hour at a speed of 200 rpm.
[0137] The obtained mixture was dried in an oven at 60°C overnight. The resulting dried
product was pyrolysed under argon atmosphere for 5 hour at 1,150°C.
[0138] After pyrolysis, the sample was recovered and milled at a speed of 400 rpm for 5
min.
[0139] The obtained powder was added to an aqueous solution containing PVA (62.5 g/L) dissolved
at 60°C. The obtained mixture was spray-dried at 100°C and a powder was recovered.
[0140] This powder was heat treated at 200°C for 16 hours under air and then pyrolysed at
1050°C for 1 hour under argon atmosphere.
EXAMPLE 5
Preparation ofa SiOC composite material in accordance with the invention
[0141] A sample of 8 g of amorphous methyl/phenyl (4/1) bridged polysilsesquioxane compound
was put in solution in 200 mL of acetone.
[0142] The solution was heated at 55°C under magnetic stirring for 10 min. A sample of 1.3
g of crystalized silicon was added to the solution. Acetone was then evaporated with
a rotary evaporator.
[0143] The obtained dried product was pyrolysed under argon atmosphere for 5 hour at 1,150°C.
[0144] After pyrolysis, the sample was recovered and milled at a speed of 400 rpm for 5
min.
[0145] The obtained powder was added to an aqueous solution containing PVA (62.5 g/L) dissolved
at 60°C. The obtained mixture was spray-dried at 100°C and a powder was recovered.
[0146] This powder was heat treated at 200°C for 16 hours under air and then pyrolysed at
1,050°C for 1 hour under argon atmosphere.
EXAMPLE 6
Preparation ofa SiOC composite material in accordance with the invention
[0147] PhSi(OMe)
3 and MeSi(OMe)
3 were both dissolved in methanol. Then, a required amount of crystallized silicon
was added to the previous mixture. The obtained solution was stirred for several minutes
at room temperature. Then, a required amount of hydrochloric acid was added and the
solution was stirred for several minutes at 60°C.
[0148] The obtained Si-loaded polysilsesquioxane material was washed and dried before pyrolysis
at 1,200°C for 5 hours under argon. After pyrolysis, the sample was recovered and
milled at a speed of 400 rpm for 30 min.
[0149] An amount of 6.25 g of solid PVA was added in the bowl and the mixture was milled
for 1h at a speed of 150 rpm. A powder was recovered.
[0150] This powder was heat treated at 200°C for 16 hours under air and then pyrolysed at
1,050°C for 1 hour under argon atmosphere.
EXAMPLE 7
Use of the materials as electrode active material
[0151] For each of examples 1 to 3, slurry containing the obtained material, carboxymethyl
cellulose (CMC) used as binder and vapor grown carbon fibers (VGCF) used as conductive
agent was coated on a 12 µm cupper foil and used as electrode.
[0152] The electrode was used in coin-cell type battery in order to evaluate the electrochemical
performance of the material. The other electrode was lithium metal. The two electrodes
were separated by a Celgard 2400 separator and the battery was filled with a LiPF
6-containing electrolyte. Electrochemical performances were evaluated at a C-rate of
C/10.
Results
[0153] Figure 5 shows the voltage profile for the first two charge-discharge cycles (obtained
from a galvanostatic measurement at a C rate of C/10 between 0.01 and 1.2 V) of the
battery prepared with the SiOC material obtained in example 1.
[0154] The electrochemical performances (capacity v/s number of cycles) of the batteries
prepared from anode materials of examples 1 to 6 are shown in Figure 6.
[0155] The anode materials using the SiOC composite materials of the invention (examples
1, 3, 4, 5 and 6) provide high capacity even after more than 20 cycles, whereas the
capacity obtained with the electrode material of example 2 not in accordance with
the invention deteriorates over time after 20 cycles.
[0156] Thus, the SiOC material of the invention provides a superior anode material for both
capacity and cycle durability.
EXEMPLE 8
Preparation ofa SiOC composite material in accordance with the invention and use as
an electrodes active material
[0157] PhSi(OMe)
3 and MeSi(OMe)
3 were both dissolved in methanol. Then, a required amount of crystallized silicon
was added to the previous mixture. The obtained solution was stirred for several minutes
at room temperature. Then, a required amount of hydrochloric acid was added and the
solution was stirred for several minutes at 60°C.
[0158] The obtained Si-loaded polysilsesquioxane material was washed and dried before pyrolysis
at 1,200°C for 5 hours under argon. After pyrolysis, the sample was recovered and
milled at a speed of 400 rpm for 30 min.
[0159] The electrochemical performances (capacity v/s number of cycles) of a battery, prepared
as described in previous example 7, from the obtained material are shown in Figure
7.
References :
[0160]
- [1] Fukui et al., Appl. Mater Interfaces, 2010 Apr (4), 998-1008 ;
- [2] Fukui et al., Journal of Power Sources, 196 (2011), 371-378 ;
- [3] Fukui et al., Journal of Power Sources, 243 (2013), 152-158 ;
- [4] Kaspar et al., Journal of Power Sources, 2012, 1-6.
1. A SiOC composite material in microparticulate form, characterized in that the microparticles are formed, in whole or in part, of an amorphous SiOC matrix,
with Si ranging from 20 wt% to 60 wt%, O from 20 wt% to 40 wt% and C from 10 wt% to
50 wt%, in which amorphous or crystallized silicon particles are embedded.
2. The SiOC composite material according to claim 1, wherein the microparticles are of
core/coating structure with a core formed of said amorphous SiOC matrix and coated
with at least one amorphous carbon layer.
3. The SiOC composite material according to claim 1 or 2, wherein the microparticles
have an average particle size ranging from 1 µm to 100 µm, in particular from 5 µm
to 50 µm.
4. The SiOC composite material according to any one of the preceding claims, having a
Brunauer Emmett Teller specific surface area ranging from 1 m2/g to 100 m2/g, in particular from 1 m2/g to 55 m2/g.
5. The SiOC composite material according to any one of the preceding claims, wherein
the microparticles have a globally spherical shape.
6. The SiOC composite material according to any one of the preceding claims, for which
an adsorption isotherm of nitrogen specified in IUPAC is classified in TYPE III.
7. The SiOC composite material according to any one of the preceding claims, wherein
crystallized silicon particles are embedded in said SiOC matrix, the crystallized
silicon having a cubic crystalline structure.
8. A method for producing a SiOC composite material in microparticulate form, comprising
at least the following steps, in that order, of:
(i) providing a product consisting of at least one silicon-containing polymer enriched
in amorphous or crystallized silicon particles;
(ii) pyrolysing the product of step (i) to yield an amorphous SiOC matrix with Si
ranging from 20 wt% to 60 wt%, O from 20 wt% to 40 wt% and C from 10 wt% to 50 wt%,
in which amorphous or crystallized silicon particles are embedded;
(iii) processing the pyrolysis product obtained in step (ii) into a powder form with
an average particle size ranging from 1 µm to 100 µm;
to obtain the desired SiOC composite material.
9. The method according to the preceding claim, comprising a subsequent step (iv) of
forming an amorphous carbon coating on the surface of the particles of the powder
obtained in step (iii) to obtain microparticles of core/coating structure.
10. The method according to claim 8 or 9, wherein the silicon-containing polymer is a
polysilsesquioxane.
11. The method according to anyone of claims 8 to 10, wherein said amorphous or crystallized
silicon particles have an average size ranging from 2 nm to 2 µm.
12. The method according to anyone of claims 8 to 11, wherein the product in step (i)
is prepared by mixing at least one silicon-containing polymer in a solid state with
a crystallized or amorphous silicon powder, in particular by mechanical milling.
13. The method according to any one of claims 8 to 11, wherein the product in step (i)
is prepared by addition of a crystallized or amorphous silicon powder to silicon-containing
polymer dissolved in a solvent, followed by spray drying or evaporation of the solvent.
14. The method according to any one of claims 8 to 11, wherein the product in step (i)
is prepared by synthesizing the silicon-containing polymer by a sol-gel method in
the presence of a crystallized or amorphous silicon powder.
15. The method according to any one of claims 8 to 14, wherein the product is pyrolysed
in step (ii) by heating at a rate ranging from 1°C/min to 30°C/min, in particular
from 2°C/min to 10°C/min, to a temperature in the range of 600°C to 1,400°C, in particular
of 900°C to 1,300°C, notably with the heating duration at final temperature ranging
from 5 minutes to 10 hours, in particular from 30 minutes to 5 hours.
16. The method according to any one of claims 9 to 15, wherein the carbon coating is formed
in step (iv) by:
(a) coating the particles with at least one organic carbon precursor containing no
silicon atoms and being able to be transformed into carbon during a pyrolysis process;
and then
(b) pyrolysing said coated particles to obtain the carbon coating.
17. The method according to the preceding claim, wherein the said carbon precursor is
chosen from polyvinylidene difluoride, sucrose, chlorinated polyethylene, polyvinyl
chloride, polyethylene, phenolic resin, polyethylene oxide, pitch, polyvinyl alcohol,
polystyrene, carboxymethyl cellulose or a salt thereof, alginic acid, oxalic acid
including sodium or potassium salt, polyacrylic acid or a salt thereof, polyacrylonitrile
and polyvinyl fluoride, preferentially said carbon precursor is a polyvinyl alcohol.
18. The method according to any one of claims 8 to 17, wherein the SiOC composite material
obtained at the end of step (iii) or (iv) is as defined in any one of claims 1 to
7.
19. Use of a SiOC composite material as defined in any one of claims 1 to 7 or as obtained
according to the method defined in any one of claims 8 to 18, as an electrode active
material, in particular for an anode electrode and more particularly for a lithium-ion
battery anode.
20. An electrode active material comprising at least a SiOC composite material as defined
in any one of claims 1 to 7 or as obtained according to the method defined in any
one of claims 8 to 18.
21. An electrode comprising an electrode active material as defined in claim 20.
22. The electrode according to the preceding claim, which is an anode electrode, in particular
a lithium-ion battery anode.
23. A battery, comprising an electrode as defined in claim 21 or 22.
24. The battery according to the preceding claim, which is a lithium-ion battery, in particular
a lithium-ion secondary battery.